1. Field of the Invention
The present invention relates to a dispersion compensation apparatus and method for compensating for the wavelength dispersion of an optical fiber in a wavelength division multiplexing (WDM) optical transmission system.
2. Description of the Related Art
In a conventional WDM optical transmission system, a fiber-type dispersion compensator referred to as a dispersion compensation fiber (DCF) is well known as a technology of compensating for the wavelength dispersion of a line fiber forming an optical transmission line. A DCF indicates dispersion having a sign inverse to that of the line fiber, and can thereby compensate for the dispersion of the line fiber. Since the amount of compensation provided by a DCF is proportional to the fiber length of the DCF, it is necessary to adjust the fiber length of the DCF depending on the dispersion of a target line fiber.
DCFs are produced by manufacturers at intervals of a fixed, specific amount of dispersion (for example, 100 ps/nm). Unfortunately, the actual amount of dispersion of a line fiber is typically not an even multiple of these intervals, thereby causing a setting error of the amount of compensation. As a result, it is very difficult to completely compensate for the wavelength dispersion of a line fiber using DCFs currently available on the market.
Furthermore, wavelength dispersion of a line fiber is wavelength-dependent, and is known to have a characteristic referred to as a dispersion slope. The dispersion slope corresponds to the inclination of the dispersion-to-wavelength graph linear-approximated in a wavelength area used for a signal light.
A DCF has a dispersion slope having a sign inverse to that of a line fiber. Based on this, the dispersion slope of the line fiber can be partially compensated for. However, since the dispersion slope of the DCF is proportional to the fiber length, both wavelength dispersion and dispersion slope of the line fiber cannot be compensated for using a DCF of a fixed length.